1. Field of the Invention
The present invention relates generally to a vapor generating device used while testing the fluid integrity of a fluid system, and more specifically to a vapor generating device that can safely produce a vapor at high pressures.
2. Description of the Prior Art
A visible vapor or smoke produced under controlled conditions which provide the ability to start and stop the vapor generation, to vary the flow of the vapor and to regulate the pressure of the vapor can be employed in many useful and beneficial ways. Such apparatus are well documented in the prior art and have been employed for various applications such as; air flow studies, theatrical effects, simulation of battlefield or structure fire conditions for training purposes, visibility obstruction, camouflage and to determine the presence and location of leaks in a vessel or conduit by observation of the vapor egress. Exemplary of such prior art systems include those disclosed in Great Britain Patent Specification 1,039,729 entitled SMOKE GENERATOR, published Aug. 17, 1996; Great Britain Patent Specification 1,064,234 entitled IMPROVEMENTS IN FLUID HEATING APPARATUS PARTICULARLY FOR SMOKE GENERATIONS OR THE LIKE, published Apr. 5, 1967; Great Britain Patent Specification 1,243,381 entitled IMPROVEMENTS IN SMOKE GENERATORS, published Aug. 18, 1971; Great Britain Patent Specification 640,266 entitled AN IMPROVED METHOD AND APPLIANCE FOR CREATING ARTIFICIAL FOG, MIST OR SMOKE, published Jul. 19, 1950; and Great Britain Patent Specification 1,258,266 entitled PROCESS OF SEALING, DETECTING AND/OR LOCATING LEAKS, published Dec. 30, 1971, the teachings of all of which are expressly incorporated herein by reference.
These apparatus utilize various materials, usually with the application of heat, to produce a dense vapor that is then admixed with a propellant gas of various type and expelled into the environment where the properties of the vapor are to be exploited. The selection of a material to vaporize is dependent on the application and environment in which the vapor is to be used. For instance, solutions of water and glycerin and glycol in various proportions are common and may be used for theatrical purposes where persons may be exposed to breathing the vapor for long periods of time and where the moisture from the water vapor will not damage the area where the vapor is applied. The chemical compound titanium tetrachloride (TiCl4) produces a fine white vapor when exposed to moisture in the air; however, the material and its vapors are highly corrosive and it must be deployed carefully and in small quantities lest the corrosiveness cause damage. Petroleum or paraffin oils such as mineral oil may be utilized in applications where a dense vapor with a long persistence (amount of time required to dissipate) is required and the application is resistant to the effects of hydrocarbons.
Most apparatuses are intended to expel vapor into the surrounding environment as when used for air flow study, visual obstruction, theatrical, and training purposes. These apparatus expel vapor at or near atmospheric pressure using a driven fan or pump, or alternately, a compressed gas such as air, nitrogen or carbon dioxide (CO2), to admix air or other gas and the vapor and propel the mixture into the surrounding area. Pyrotechnic devices are also used in such applications but lack the useful control abilities described previously.
Furthermore many applications exist where the vapor is injected into a closed vessel or conduit for the purpose of determining the presence and location of an opening or leak in the vessel or conduit. The injection pressure of the vapor must be controlled in these applications as excessive pressure may damage the vapor generating device or the vessel or conduit into which the vapor is injected.
One such application is the determination and location of leaks effecting the operation of internal combustion engines and the pollution causing emissions of the engines and associated systems. For instance, leaks in the fuel vapor recovery system (commonly known as the EVAP System) utilized with gasoline powered passenger vehicles are known to be a significant source of hydrocarbon pollution as the leak allows raw hydrocarbon evaporating from the fuel to escape to the surrounding atmosphere. A common method for locating the leak within this system is to inject a suitable vapor into the system and observe for the vapor egress. Since the system is initially designed to handle hydrocarbon fuels, a vapor produced by heating mineral oil, also a hydrocarbon, is typically used to assure compatibility. However, one must take care in pressurizing this system as most are designed to contain a maximum of one pound per square inch (1 PSI). Additionally, the US Environmental Protection Agency specifies an inspection test pressure of 12 to 14 inches of water column (approximately 0.47 PSI). There is a plurality of products available that conform to these requirements.
A second common application is the detection and location of leaks in an internal combustion engine's fuel and air induction system. Such leaks upset the delicate ratio of fuel to air induced into the engine reducing the engine's performance and efficiency while increasing pollution causing emissions. Various devices and apparatus are well known in the art and products conforming to the requirements for testing fuel vapor recovery systems are very capable of performing an inspection of most induction systems. Some apparatus employed for this application can develop pressures as high as 2 PSI and are therefore not suitable for fuel vapor recovery system inspection.
Internal combustion engine technology is advancing to improve performance and efficiency. One method coming into common usage is to increase an engine's fuel and air induction system pressure. Normally this system is in vacuum or negative pressure drawing fuel and air into the combustion chamber. This type of engine is known as a vacuum induced or self aspirated engine. To increase the induction system pressure a turbocharger which utilizes exhaust gas pressure to rotate an impeller that in turn rotates a second impeller, imparting energy and thus pressure to the induction system air stream is commonly employed and can increase the induction system pressure to as high 30 PSI. This forces a greater quantity of fuel and air into the combustion chamber where a greater quantity of energy can be derived from the fuel.
In a forced induction engine, induction system leaks are more critical then in vacuum induced engines and thus must be detected, located and repaired to assure the highest possible performance and efficiency. The devices and apparatus developed for the inspection of fuel vapor recovery and vacuum induction systems are not always adequate for use in a high pressure forced induction system. Elastic connections between components may remain sealed under the low pressures of 0.47 PSI to 2 PSI. However, these connections will dislocate and leak when exposed to the higher pressure of the forced induction system.
Thus there is a need for a vapor generating device that can safely produce a controlled vapor at pressures up to and exceeding 30 PSI. Additionally this vapor must be compatible with all systems of, and used in conjunction with, internal combustion engines. To assure system compatibility, mineral oil vapor is the preferred choice. However when mineral oil vapor is subjected to the combination of elevated pressure and the high temperature required to produce the vapor, spontaneous combustion or dieseling is prone to occur, causing significant damage to the vapor generating apparatus and possibly the engine and vehicle to which it is connected.
Significant prior art exists teaching the use of inert gas propellants such as nitrogen (N2) or carbon dioxide (CO2) to eliminate the oxidizing effect of air and thus inhibit the ignition of the vapor within the vapor generating apparatus. Exemplary of such prior art references include the aforementioned prior art, and in particular Great Britain Patent Specification 640,266 that generates smoke by projecting an atomized spray of glycerin, oil or other liquid by means of a jet of carbon dioxide or nitrogen under pressure onto a surface, such as the wall of a cylinder, heated to a temperature sufficiently elevated to cause immediate vaporization of the liquid. In fact, much of the prior art teaches that there is a real potential for fire or explosion if inert gas propellants are not used, as suggested by aforementioned Great Britain Patent Specifications 640,266 and 1,039,729 as well as U.S. Pat. No. 6,526,808 entitled SMOKE AND CLEAN AIR GENERATING MACHINE FOR DETECTING PRESENCE AND LOCATION OF LEAKS IN A FLUID SYSTEM, the teachings of which are likewise incorporated by reference.
However, the storage and use of gases under high pressure presents a significant hazard in the working environment of an engine service facility. There is a genuine danger of asphyxiation should a leak occur in a closed environment and many deaths have been documented. Additionally failure to properly store, handle and transport the high pressure storage vessels can result in damage to the storage vessel causing it to become a projectile capable of penetrating a masonry wall. Obviously an object with this amount of energy is capable of causing great bodily harm and property damage. Further there is a significant added expense to purchasing and storing these gases and the dangers and costs are compounded because of the large quantities required to support the large flow rates produced with the higher pressures.
Thus there is a further need for a vapor generating apparatus that can safely produce vapor, of a composition such as mineral oil, at higher pressures while utilizing compressed air as the propellant.
One method used since the early 2000's is to employ a pressure sensing device such as a pressure switch to extinguish the heat source when pressures within the vapor generating chamber exceed approximately 5 PSI. The pressure continues to increase to the desired inspection pressure but the extinguished heat source begins cooling quickly and combustion of the vapor is prevented. Although this is an effective method it also results in a decreased vapor density at the desired test pressure. A lower density vapor is less visible and therefore less effective for the purpose of leak identification and location. A similar technique commonly utilized is to first fill the vessel or conduit with vapor and then apply compressed air to reach the desired test pressure. This technique results in the same less effective lower density vapor.
As is apparent from the foregoing, there is a need in the art for a vapor generating device for safely generating vapor for use in high pressure fluid systems. The present invention addresses this particular need, as will be discussed in more detail below.